1. Field of the Invention
The present invention relates to a printing head for ejecting ink and an ink jet printing apparatus that carries out printing using the printing head, and in particular relates to a head configuration to cope with deformation of component members of a printing head due to thermal load applied to the corresponding printing head.
2. Description of the Related Art
Various types of printing heads have been known. FIG. 9A and FIG. 9B are perspective views showing a print cartridge, in which a printing head and an ink container according to a prior art example are integrally composed, when being observed from the underside of the cartridge on which nozzles are arrayed, and from the upside opposed thereto, respectively.
In FIG. 9A and FIG. 9B, the print cartridge 601 is such that the printing head portion including a printing element substrate 702 and an ink container portion, in which ink is stored, are composed to be integral with each other. The printing element substrate 702 is composed of a heater operating as an energy generating element for converting electric energy to thermal energy, a substrate provided with circuit wiring for supplying electric energy supplied from the printing apparatus body to the heater, and a nozzle plate provided with a flow path for supplying ink to the heater and an ejection orifice through which ink is ejected.
In the present prior art example, one printing element substrate 702 is provided with ejection orifice arrays 703, 704, and 705 for ejecting inks of three colors which are yellow, magenta, and cyan, respectively.
An electric wiring substrate 706 is provided with wirings for transmitting electric signals from the printing apparatus body to the printing element substrate 702, and is provided with an external signal-inputting terminal 707 for inputting electric signals from the printing apparatus body at the end part thereof. The end part, at the side opposite to the external signal-inputting terminal 707, of the electric wiring substrate 706 is electrically connected to two end faces of the printing element substrate 702. And, the electrical connecting portion is covered with a sealing member 708, so that the electrical connecting portion is protected from ink that may be adhered to the surface of the printing head portion.
The ink container portion in which ink to be supplied to the printing element substrate 702 is stored is formed so that a cover 710 is provided on a casing portion 709 and partitions (not illustrated) for dividing ink-by-ink chambers are provided inside the casing. Accordingly, the ink storing portion for individually storing inks of respective colors consisting of yellow, magenta and cyan is constructed. Ink absorbers for retaining inks are accommodated in the ink storing portions of these ink colors, respectively. In addition, ink supplying path for each of colors of ink is provided on the bottom portion of the casing portion 709. Ink can be supplied to the printing element substrate 702 via these ink supplying paths. The ink supplying paths are provided with a filter by which foreign substances can be prevented from entering the ejection orifices.
FIG. 10 is a sectional view taken along the line X-X in FIG. 9A, and shows the configuration of the printing element substrate of the printing head portion and the surroundings thereof. In FIG. 10, the printing element substrate 702 is illustrated in a state where the nozzle plate is removed and a heater, etc., on the same substrate is omitted. A supporting substrate 802 for supporting the printing element substrate 702 is provided with an ink supplying port 803 for supplying inks of respective colors, which are accommodated in the ink containers. The supporting substrate 802 is molded by using an alumina material and polishing the same. Accordingly, the printing element substrate 702 is adhered and fixed at high accuracy. Further, the supporting plate 804 fixes and supports the electric wiring substrate 706 and is made of the same material as that of the supporting substrate 802. A sealing material 805 such as resin is used to seal a portion between the printing element substrate 702 and the supporting plate 804. One of the reasons is to protect the wall of the printing element substrate 702 from ink. It is common that thermo-hardening type resin, which is comparatively easily handled in the production process, is used for the sealing material.
Now then, in the above-described printing head, there may be a case where the printing head is influenced by heat in production and actual use, and the head composing member is subjected to deformation. To cope with such deformation, various constructions have been conventionally employed. In Japanese Patent Application Laid-open No. 10-044420 (1998), it is described that the printing element substrate is adhered to and fixed at a supporting member via a supporting substrate whose thermal properties are almost the same as those of the printing element substrate. This construction allows deformation and breakage of the head to be prevented, which are caused by a difference in the thermal expansion ratio due to a change in temperature of the composing member of the printing head such as the printing element substrate. In addition, another composition for preventing harmful thermal effects such as deformation in the printing head has been well known, which prevents a difference in the linear expansion ratio by adhering a supporting substrate such as alumina between the printing element substrate and the supporting member.
Also, Japanese Patent Application Laid-open No. 2002-019119 discloses the printing element substrate and the supporting member thereof employing materials whose linear expansion ratios are equivalent to each other. According to this construction, it is possible to reduce the thermal deformation due to a difference in the thermal expansion ratio. Further, in order to increase the rigidity of the printing element substrate, it can be considered that the thickness is increased, or the surface area thereof is further widened to withstand against the thermal deformation.
However, in any one of the above constructions, such a problem is brought about, which increases the production costs of the printing head. To the contrary, such a type in which a resin material is used for the supporting member has an advantage in that it can be inexpensively produced. However, it has a problem regarding the thermal deformation as described below.
That is, where the supporting member of a resin material and the printing element substrate are adhered together by a thermal hardening type adhesive agent, the hardening temperature is made higher than the room temperature. That is, the supporting member and the printing element substrate are adhered to each other in a state where they are further expanded than in the room temperature, and after they are adhered, the respective members are caused to shrink with a lowering in the temperature of the printing head. In this case, where the supporting member is a resin material as described above, the linear expansion ratio of the supporting member is larger than that of, for example, a silicon material of the printing element substrate. Therefore, the shrinking ratio of the supporting member becomes larger than that of the printing element substrate when the temperature of the printing head is lowered after adhesion. As a result, a dimension change of the supporting member becomes greater than that of the printing element substrate when the temperature of the printing head immediately after the adhesion gets back to the room temperature, and then a stress is caused between the printing element substrate and the supporting member. In this case, there may be a case where the printing element substrate is greatly deformed without resisting stress generated. And, the ejecting direction of ink that is ejected from a printing head subjected to such deformation is biased, and the landing position of ink shifts to cause the printing quality to be lowered. Further, there may be a case where the members that compose the printing head such as the printing element substrate are broken by the deformation.
In addition, a similar problem occurs when the temperature of the printing head rises during a printing operation. When the temperature of the printing head rises by an ejecting action during printing, the printing element substrate and the supporting member expand to cause their dimensions to be increased. As described above, the linear expansion ratio of the supporting member is larger than that of the printing element substrate, and then a change in the dimension of the supporting member becomes larger. As a result, there may be a case where stress is brought about between the printing element substrate and the supporting member, and a problem similar to the above occurs.